1. Field of the Invention
This specification teaches a new method for disinfecting and sterilizing air, surfaces of all types and food from microorganisms and toxic chemical substances. More particularly, it relates to a process and apparatus for protecting surfaces in closed or captured environments (zones) from external sources of microbial contamination in an efficient and cost effective process. These zones can be large volumes such as high rise building, cruise ships and jet airliners, or small volumes such as small rooms or surgical operation areas whether in a hospital operating room or on the battle field.
2. Description of the Related Art
All prior art for sterilizing and disinfecting air has been based on using commercially available ultra-violet (UV) lamps or by using magnetic fields. These lamps are either pulsed or continuous. Continuous lamps are mercury based and emit principally at 254 nm. A number of companies are presently producing UV light based apparatus for the destruction of virus, bacteria, spores and pathogens (microorganisms or VSP) that are in room air. This is an effective treatment because it continually exposes room air currents to the treatment light and over time has sufficient exposure time to treat VSP's. The required exposure times range from 10's to 100's of seconds, depending on the light absorption capability of the different virus and bacteria at the 254 nm. While this is effective for treating the room air of individual rooms, it requires long treatment times to be effective for treating large flowing volumes of air that pass quickly down large ducts. Long treatment time is impractical for treating most surfaces.
Magnetic based apparatus also require time to deactivate or destroy these VSP's. Two such inventions are directed to specific applications. Wesley, U.S. Pat. No. 4,458,153 is directed specifically towards liquid like substances enclosed in pipes, but does not discuss any test results. Sangster, U.S. Pat. No. 5,750,072 requires an injection of a sterilizing fluid as a mist or vapor for the magnetic field to produce radicals that in turn are used to alter the VSP's. He does not discuss any test results. Hofmann, U.S. Pat. No. 4,524,079 is directed specifically to treating food stuffs. He speaks of requiring up to 100 pulses at frequencies ranging from 5 to 500 kHz. None of these patents are admitted to being prior art by their mention in this background section. Although the action time would be short, the power required to treat large areas and the apparatus design limit its practical application.
The broad ultraviolet spectrum had been divided into three regions depending on its different effects on biological systems. Reference to these regions are predominantly made in medical terminology with UV-A defined as a range or band between 320 nm and 400 nm, UV-B defined as a band between 280 nm and 320 nm, and UV-C defined as encompassing wavelengths shorter than 280 nm. Photochemists and photobiologists do not generally use these terms because absorption spectra of chemical bonds are much narrower than these generally defined bands. Instead, they use the wavelength of the applied radiation to correlate the observed effects.
Claims have been made that germicidal UV-C radiation is used to deactivate DNA. This is because the mercury lamp emission at 254 nm is close to a good DNA absorption band. None of these claims make reference to any shorter wavelengths and to the primary DNA protein absorption band that peaks at 200 nm (see FIG. 9). In fact, all literature directs researchers away from using any shorter wavelengths due to the high absorption of molecular water. Mercury lamps are used for wastewater treatment and work well for this application. However, this specification teaches that since we do not live underwater, the protein absorption band offers much more significant action spectra that can be used to kill and deactivate the DNA of microorganisms more effectively. This concept is a significant advancement and a step change in the technology used for sterilization and disinfection.
During the past few years, new UV emitting lamps based on the excitation of excimers are becoming commercially available. These emitters produce single line or narrow spectral emission at a wavelength determined by the gas composition of the lamp. If the treatment lamp's wavelength is chosen to match closely to the peak of absorption of the microorganism's DNA, then a lethal dosage can be delivered to the VS P's in a shorter time. No patent has been found that teaches the use of new ultra-violet (NUV) sources coupled with supporting equipment that can effectively and efficiently disinfect and sterilize large volumes of air, large and small surfaces, and food stuffs in various stages of preparation.
In this specification, sterilization or sterilize refers to sterilization or high level disinfectant as defined by US FDA. The terms disinfectant and disinfection refers to all other levels of disinfection.
NUV Background
The genetic makeup of all living organisms is contained in their DNA molecule. Replication occurs by the splitting of the DNA molecule, which duplicates itself through a transformation of its structure. Parts of the DNA molecule have been given names such as pyrimidine bases, cytosine, thymine or uracil that form a group of biochemicals that sustain life. The long DNA molecule holds itself together by using simple bonds like those found in sugars.
Researchers believe that the energy of the germicidal UV photon causes the formation of a strong (covalent) bond to develop between specific biochemicals. However, the bond strength of the covalent bond is very dependent on the relative position of the participating atoms. When the bond is symmetrical on both sides of a hydrogen atom in the bond, it is referred to as a dimer. A dimer is a very strong bond and is not generally broken during the vaporization of the liquid. Germicidal UV light is known to produce Thymine, cytosine-thymine, and cytosine dimers. After the formation of the dimer, further replication of the DNA stops. FIG. 8 shows the concept of the dimer formation in a DNA molecule.
The DNA molecule absorbs light from about 180 nm to about 4300 nm. The most effective wavelength in water is about 254 nm because water absorption increases steadily as the wavelength decreases below 240 nm. DNA absorption also increases with lower wavelength. FIG. 9 graphically shows this relationship (Von Sonntag; Disinfection by free radicals and UV-radiation. Water Supply 4, 11-18 (1986)).
The commercial germicidal light source for UV irradiation near the 260 nm absorption peak of DNA has been produced by using mercury as the source for generating photons. The mercury gas and its pressure in the lamp determine the wavelength of the emitting light. For low-pressure (LP) and low-pressure high output (LPHO) lamps, the emitting wavelength is 254 nm. For medium pressure lamps, the emission ranges from 200 nm to above 300 nm. However, the strength of the emitted light is not effective below 245 nm for the continuous emitting lamps and below 235 nm for medium pressure lamps. Xenon gas in pulsed lamps produces a similar emission as the medium pressure mercury lamps.
DNA action spectra show that absorption increases as the wavelength decreases, with a relative maxima at 260 nm and largest at 200 nm. Many articles indicate the principal action spectra of the DNA absorption is from 245 to 280 nm range and do not address the 200 nm peak. Since water absorption significantly increases below 235 nm, it becomes apparent that DNA effectiveness curves that omit the 200 nm peak apply only to organisms in water.
MS-2 Phage is a marker virus that is used to measure reproduction viability after germicidal UV irradiation. FIG. 10 is DNA absorption without the influence of water (Gates, F. L. A study of the bactericidal action of ultra violet light III. Jour. General Physiology 14, 31-42 (1930)). Absorption is more than doubled at 222 nm.
A recent technical paper (Peak et al, UV action spectra for DNA dimer induction. Photochemistry and Photobiology, 40, 5 (613-620), 1984) suggests that dimer formation is not the only requirement to inactivate DNA. Absorption of other molecular groups in the long DNA chain increase as the wavelength is reduced from 254 nm. Damaging or destroying these bonds may be more effective in deactivating the DNA than compared to the 254 nm band. No one has done a detailed study of the effectiveness of inactivation for the different single line UV emitters that are produced by the new UV source (NUV) excimer lamps. Reports show that damage caused by 254 nm light can be reversed by longer wavelength UV and blue light (FIG. 12). 222 nm photons with their higher energy are not expected to cause this ‘photo-reactivation’ phenomenon. However, this theory needs to be confirmed.
An excimer lamp emitting at 222 nm is considered the most effective source because DNA chains and biochemicals have greater absorption at this wavelength. The steep rise in absorption below 250 nm is exhibited by all proteins and most nitrogenous bases. It has been fairly well established that the peptide bonds are responsible for the steep rise in absorption exhibited by all proteins. A similar increase in absorption at lower wavelengths occurs as well for nucleo-proteins, aromatic amino-acids, diglycine, triglycine, and bovine albumin (McLaren, et al, Photochemistry of Proteins and Nucleic Acids, Pergamon Press, Macmillan Company, 1964). An organic chemist suggests that this lower wavelength is more effective in breaking bonds and producing dimers in the purine bases and sugar phosphates instead of the pyrimidines. The 222 nm is not strongly absorbed by water vapor and oxygen in the air. A shorter wavelength would be most certainly rendered ineffective by water vapor and oxygen absorption for long irradiation distances in air. Shorter wavelength radiation would significantly increase the production of ozone that is harmful to humans and animals.
Tests
Using a lamp that emits 222 nm, a comparison test with and without water was made to determine the effect of this radiation on organisms. The organism used in all tests was the MS-2 virus, which has become a standard indicator of mutation effectiveness. The EPA report (811-R-96-002) reports a 4.3 average log reduction of the MS-2 virus using mercury light 254 nm at an irradiance greater than 128 mj/cm2.
Three wavelengths were tested: 222, 253, 259 nm. The 222 nm lamp was tested at three levels of irradiance with the virus in a thin layer of water in order to reduce the absorption effect of water. A separate test was also done with the virus in more water. The 253 and 259 nm lamps were tested at the identical irradiance levels with the virus in water. Controls were made on all tests and a single test dish on each lamp was made to check experimental error.
The 222 nm lamp (FIG. 11) produced log 5 reductions at 40 mj/cm2 and log 6.5 reductions at 60 mj/cm2. The water test produced a 3.2 log reduction, which matched the equivalent calculated irradiance in air. The 253 and 259 nm lamps produced about log 4 reductions at 60 mj/cm2. A 3 million reduction in population is about 10 to 100 times more effective than reported mercury 254 nm results at the same irradiance.
Analysis
The results of the test indicate that 222 nm light is very effective in causing mutations in organisms. These tests indicate an improvement of between 10 to 1000 times, depending on the intensity of the lamp. It is important to note the improvement of the 259 nm source compared to the 254 nm source. It produced a 10 times improvement in the test sample. This improvement illustrates the importance in using a UV photon emitter that is near the absorption peak of the DNA or targeted chemical such as nitrogenous bases, proteins, nucleic acids, or amino-acids.
It is important to note that DNA biochemicals will have different absorption spectra and the peak absorption will be shifted by water, pH, temperature, previously absorbed light and surrounding contaminates in the air. The presence of ozone can significantly reduce the resistance to damage and shorten the action kill time. For some applications, ozone is produced to improve the killing or deactivating efficiency.
For example, tyrosine has a relative maximum at 275 nm, a red shift of 20 nm from the normal DNA curve. The tobacco mosaic virus peaks at 265 nm, but its X-protein at pH 7.3 peaks at 280 nm while the RNA peak occurs at 260 nm. Critical to the destruction of the organism is targeting the proper biochemical so the critical dosage can be delivered in the shortest time. The critical dosage is that dosage that destroys or deactivates the organism and prevents its replication.
The excimer lamp is a coaxial design that can be made as small as a pencil to as large as 1 meter long. Lamp efficiency is about the same as mercury at 10-25% wall power to UV emission. The design has several advantages over mercury lamps. Most important is that its gas can be chosen to maximize its emission to the absorption peak of the targeted biochemical. Unlike the mercury lamp, the excimer intensity can be varied from near zero to maximum. It will produce 10 to 1000 times more intensity than mercury, depending on the lamp dimensions, and it does not use mercury that will soon become regulated by the EPA.
The energy of the emitted photon is determined by its wavelength. Photon energy is about 5 ev at 250 nm and increases for shorter wavelengths. Different bonds in the DNA will be affected with photons of different energy.
FIG. 12 illustrates the 254 nm dose required to deactivation different VSP's. The bars represent with (solid) and without (open) photo-reactivation. Note that a dose of 75 mj/cm2 is required to deactivate the MS2 Phage virus and prevent photo-reactivation. In the tests shown in FIG. 11, half the dose at 222 nm was just as effective as the higher dose at 254 nm. Even though the sample was under water, the 222 nm radiation was still more effective than 254 nm radiation.
The 222 nm photon has more energy and is absorbed by S—N, S—O, O—O, O—H, and many carbon bonds that do not absorb 254 nm. This suggest that 222 nm light may also prevent DNA repair that has been reported for low level 254 nm UV sources.
Toxic Gas Weapons
Biotoxins and nerve agents can be used by terrorists as weapons against groups of people. Nothing economical has been developed that could mitigate an attack and prevent the loss of life and incapacitation at the point of attack. While government agencies of the US have developed detectors that could be used in the future to warn people in the confined areas that are under attack, nothing would prevent the attack from being effective.
Biotoxins and nerve agents are organic molecules that contain either DNA or have long chain carbon based molecules. Both of these are susceptible to destruction using NUV light sources. 222 nm will destroy the C═C and C═O bonds causing the destruction of the chemical.
The most effective means for delivery of these agents is to spread them in a gas phase through the air ventilation system. A detector would be used to turn on sufficient NUV sources so that the agents are destroyed before exiting the ventilation system into the confined area where the captured population is present. Tests still need to be done in regulated and controlled laboratories to develop the criteria for these sources to be effective and become the first line of defense. However, the concept of using the NUV source as well as the associated support equipment used for treating VSP's is valid and is also contained in the scope of this specification.
Support Equipment Contained in the Apparatus
Important to the sterilization and disinfecting apparatus is the use of a high E field electrostatic precipitator (ESP). FIG. 13 compares the range of effectiveness with mechanical filters for different pollutant sizes. As illustrated in the fourth column, it is capable of removing VSP's. However, since it can also capture fog and mist, it has the ability to breakdown ozone O3 into oxygen. Its use prevents levels of ozone from exceeding the EPA exposure safe levels.
The apparatus includes a humidification system to provide and maintain minimum moisture content at predetermined and controllable levels. In addition, the apparatus contains baffles and zone restriction devices that enhance the zone protection and minimize the positive pressure required to maintain the protected zone.